A sketch representing the modification of $r^*_\mathrm{core}$ into $r^*$ (dash-dotted lines), due to the presence of resonances (gray disks), decaying into the particles of interest (blue disks). The coordinate system is determined by the rest frame of the two daughters and consistent with Eq. \ref{eq:CFsourcewf}, where $k^*$ represents their momenta (solid blue lines). The blue dotted lines represent the remaining decay products, which are assumed to be single pions. In case of a primordial particle in the initial state instead of a resonance, the latter is not considered ($\vec{s}^*_\mathrm{res,i}=0$).